Patent Application
20070149880
Methods and apparatuses for sealing vascular punctures and openings are disclosed. More specifically, systems and methods are disclosed to determine an accurate location of the vascular opening being treated so that energy delivered by a high intensity focused ultrasound (HIFU) device is accurately delivered to the opening with minimal damage to surrounding tissue and discomfort for the patient.
Various surgical procedures are performed by medical specialists such as cardiologists and radiologists, utilizing percutaneous entry into a blood vessel. To facilitate cardiovascular procedures, a small gauge needle is introduced through the skin and into a target blood vessel, often the femoral artery. The needle forms a puncture through the blood vessel wall at the distal end of a tract that extends through the overlying tissue. A guide wire is then introduced through the bore of the needle, and the needle is withdrawn over the guide wire. An introducer sheath is next advanced over the guide wire. The sheath and guide wire are left in place to provide access during subsequent procedures.
The sheath facilitates passage of a variety of diagnostic and therapeutic instruments and devices into the vessel and its tributaries. Such diagnostic procedures may include angiography, intravascular ultrasonic imaging, and the like. Typical interventional procedures include angioplasty, atherectomy, stent and graft placement, embolization, and the like. After a procedure is completed, the catheters, guide wire, and introducer sheath are removed, and it is necessary to close the vascular puncture to provide hemostasis and allow healing.
The common technique for achieving hemostasis is to apply pressure, either manually or mechanically, on the patient's body in the region of the tissue tract and vascular puncture. Initially, pressure is applied manually and subsequently is maintained through the use of mechanical clamps and other pressure-applying devices. While effective in most cases, the application of external pressure to the patient's skin presents a number of disadvantages. For example, when applied manually, the procedure is time-consuming and requires the presence of a medical professional for thirty minutes or more. For both manual and mechanical pressure application, the procedure is uncomfortable for the patient and frequently requires the administration of analgesics to be tolerable.
Moreover, complications from manual pressure application are common. The application of excessive pressure can occlude the underlying artery, resulting in ischemia and/or thrombosis. Even after hemostasis has apparently been achieved, the patient must remain immobile and under observation for hours to prevent dislodgment of the clot and to assure that bleeding from the puncture wound does not resume. Renewed bleeding through the tissue tract is not uncommon which can result in hematoma, pseudoaneurisms, and arteriovenous fistulas. Such complications may require blood transfusion, surgical intervention, or other corrective procedures. The risk of these complications increases with the use of larger sheath sizes, which are frequently necessary in interventional procedures, and when the patient is anticoagulated with heparin or other drugs.
As a result, several alternatives to the manual pressure hemostasis technique have been proposed to address the problem of sealing vessel wall opening following percutaneous transcatheter procedures. For example, bioabsorbable, thrombogenic plugs comprising collagen and other materials have been used at the vessel wall opening to stop bleeding. These large hemostasis plugs stimulate blood coagulation at the vessel opening, but they block the catheter entry tract, making catheter reentry difficult, if needed. Other techniques provide for the use of small dissolvable disks or anchors that are placed in the vessel to block or clamp the opening. However, these devices are problematic as any device remaining in the vessel lumen increases the risk of thrombus formation. Such devices also can detach and cause occlusion in a distal section of the blood vessel, which would need to be surgically removed.
Additional techniques use needles and sutures delivered through catheters are used to ligate the opening. Obviously, this suturing procedure requires a high level of skill and suture material left in the vessel may cause tissue irritation that will prolong the healing process. Another technique involves the injection of a procoagulant into the opening with a balloon catheter blocking inside the vessel lumen. However, it is possible for the clotting agent to leak past the balloon into the vessel lumen and cause stenosis. Lasers and radio-frequency (RF) energy have also been used to thermally fuse or weld the punctured tissue together. Other more recent techniques involve the use of high frequency ultrasound (HIFU) energy.
HIFU seals vascular openings by quickly increasing the temperature of surrounding tissue by 70-90° C. in a matter of seconds. The temperature rise mobilizes and denatures collagen, forming coagulum, which rapidly seals the opening.
However, alternatives for accurately delivering a HIFU dose is desirable. Two examples can be found in U.S. Pat. No. 6,656,136 and U.S. Patent Application Publication Nos. 2004/0106880 and 2005/0080334, all of which are incorporated herein by reference. The methods and apparatuses disclosed herein are further contributions to the art of accurately navigating and dosing HIFU energy at a vessel opening to seal the opening with minimal damage to surrounding tissue or discomfort for the patient.
In satisfaction of the aforenoted needs, a medical system is disclosed that comprises a probe comprising a distal end, at least one transducer mounted on the distal end of the probe, and a high intensity focused ultrasound (HIFU) device comprising a therapeutic array, an imaging array, at least three transducers mounted around the therapeutic array, and related processing circuitry. The transducers on the probe and on the HIFU device generate acoustic energy that passes through the tissue. The acoustic energy is converted to electrical signals by transceiver circuitry, and the electrical signals are used to produce time-of-flight (TOF) measurements, which, in turn, are used to generate a three-dimensional position of the end of the probe with respect to the HIFU device and the therapeutic array of the HIFU device.
The transducer(s) on the end of the probe is preferably used as a transmitter and the transducers mounted on the HIFU device are preferably used as receivers so that multiple TOF measurements may be simultaneously made for each transducer on the HIFU device vis a vis the end of the probe. The three dimensional position of the end of the probe may be calculated from the TOF measurement data using a multi-dimensional scaling (MDS) algorithm or other suitable algorithm that will be apparent to those skilled in the art. The processing circuitry may also calculate local coordinates of the distal end of the probe relative to the imaging and therapeutic arrays using a Procrustean similarity transform (PST) or other suitable algorithm that will be apparent to those skilled in the art.
Using the imaging array and the acoustic data generated from the use of the transducers, the distal end of the probe can be guided into the vessel opening and the focus point of the HIFU device can be adjusted to match the three-dimensional position and the coordinates of the distal end of the probe so the operator is assured that the HIFU focus point is accurate and not out of plane. With currently available technology, independent confirmation that the plane of the HIFU focus matches that of the vessel opening is not possible.
In a refinement, the transducer at the end of the probe is a pressure transducer as well as an acoustic transducer or the probe tip may include separate acoustic and pressure transducers. In a related refinement, one of the transducers at the end of the probe is polyvinylidene difluoride (PVDF) piezo electric film transducer, a polyvinylidene fluoride (PVF) piezo electric transducer or a piezo electric copolymer transducer. Copolymer piezo electric transducers are often copolymers of vinylidene fluoride, but the use of other copolymers are possible. In such an embodiment, the use of an imaging array may be eliminated or rendered superfluous as the vessel opening may be located using the pressure sensing capabilities of the probe tip. In short, a pressure change as the probe tip enters the vessel opening is detected.
In another refinement, the at least three reference transducers fixedly mounted around the therapeutic array comprise four transducers. For more efficient TOF calculations, these four transducers are used as receivers and the at least one transducer at the probe tip is used as a transmitter. In a related refinement, the transducers may be of the ceramic type, the PVDF type or the piezo electric copolymer type.
In another refinement, the MDS performed by the control circuitry or software is performed multiple times for different sets of three transducers mounted around the HIFU device. In the event a large discrepancy is generated due to a noisy or defective transducer, use of that noisy or defective transducer in fiture calculations can be stopped. In related refinement, the results of the MDS calculations are averaged.
In another refinement, the controller, processor or control circuitry or software calculates a focal depth for HIFU therapy based on the PST or use of a similar algorithm.
In another refinement, the device generates an alarm if the therapeutic array is displaced laterally or longitudinally from the distal end of the probe by a distance greater than a predetermined threshold distance.
A method for locating a vessel opening or puncture is also disclosed. One disclosed method that utilizes pressure readings at the probe tip comprises:
placing a HIFU device with at least three transducers mounted thereon on a patient's body above the vessel opening;
inserting a probe through a skin puncture site and moving a distal end of the probe towards the vessel opening, the distal end of the probe being connected to at least one probe acoustic transducer and at least one pressure transducer or at least one combination acoustic/pressure transducer;
transmitting acoustic energy through the patient's tissue and between the probe transducer and at least three reference transducers mounted on the HIFU device;
converting acoustic energy received at either the probe transducer or the transducers mounted on the HIFU device to electrical signals and generating TOF measurements from said electrical signals;
generating three-dimensional position data for the end of the probe based on the TOF measurements;
generating local coordinate data based on the three-dimensional position data;
determining when the probe tip is at or near the opening in the vessel by changes in fluid pressure sensed by the pressure transducer;
calculating a final local coordinate position of the distal end of the probe with respect to the imaging and therapeutic arrays based on the TOF measurements and the three-dimensional position data; and
calculating a focal point of the HIFU therapeutic array based on the final local coordinate position.
Another method for locating a vessel opening or puncture that utilizes an imaging array comprises:
placing a HIFU device with at least three transducers mounted thereon on a patient's body above the vessel opening;
inserting a probe through a skin puncture site and moving a distal end of the probe towards the vessel opening, the distal end of the probe being connected to at least one probe transducer;
transmitting acoustic energy through the patient's tissue and between the probe transducer and at least three reference transducers mounted on the HIFU device;
converting acoustic energy received at either the probe transducer or the transducers mounted on the HIFU device to electrical signals and generating TOF measurements from said electrical signals;
generating three-dimensional position data for the end of the probe based on the TOF measurements;
generating local coordinate data based on the three-dimensional position data;
generating signals from an imaging array indicative of locations of the probe and surrounding tissue and generating video images of the distal end of the probe and surrounding tissue based on the signals from the imaging array;
manipulating the probe and the HIFU device to place the distal end of the probe at or near the opening in the vessel while viewing the video images and confirming the distal end of the probe is in a common plane with the imaging array based on the three-dimensional position data and/or local coordinate data;
calculating a final local coordinate position of the distal end of the probe with respect to the imaging and therapeutic arrays based on the TOF measurements and the three-dimensional position data; and
calculating a focal point of the HIFU therapeutic array based on the final local coordinate position.
In a refinement, the three-dimensional position data for the end of the probe is calculated using an MDS algorithm or other suitable algorithm.
In a refinement, the local coordinates of the distal end of the probe are calculated using a PST algorithm or other suitable algorithm.
In another refinement, the method further comprises removing the probe and applying HIFU energy at the final local coordinates using a therapeutic array.
In another refinement, the transducers are acoustic transducers and the at least three transducers on the HIFU comprise four reference transducers. In a related refinement, the HIFU transducers are uses as receivers and the probe transducer is used at a transmitter.
In another refinement, the method comprises performing an MDS multiple times for different sets of three of the four reference transducers mounted on the HIFU device. In another related refinement, the method further comprises averaging the results of the multiple MDS calculations. In another refinement, data from a noisy, defective or malfunctioning transducer is excluded from the calculations.
Other advantages and features of the disclosed embodiments and methods will be best understood upon reference to the accompanying drawings and detailed description that follows.
The disclosed systems and methods will be described more or less diagrammatically in the accompanying drawings, wherein:
It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are illustrated using diagrammatic representations and fragmentary views. In certain instances, details may have been omitted which are not necessary for an understanding of the disclosed embodiments or which render other details difficult to perceive. It should be understood, of course, that the sample shaking apparatus is not necessarily limited to the particular embodiments disclosed herein.
Ultrasound can be brought into a tight focus at relatively short distances from the source or origin. If ultrasound with a sufficient energy is radiated into animal tissue, cells located within the focal volume or plane or rapidly heated while surrounding tissues are unaffected. The surrounding tissues are unaffected primarily because ultrasound energy outside of the focal volume is of a low density and therefore the heating of the surrounding tissues is minimal and low impact.
High-intensity focused ultrasound (HIFU) applications utilize ultrasound intensities in excess of 1,000 watts/cm2. At a focal point, these intensities can result in large, controlled temperature rises within a matter of seconds. These large, controlled temperature rises are useful in sealing holes or punctures in blood vessels. Specifically, when accurately targeted on a vascular opening, HIFU has been shown to induce hemostasis in less a minute. In addition to blood vessel punctures, HIFU can be used in the treatment of other lacerations as well.
The mechanism of the hemostasis induced by HIFU involves the denaturization of perivascular collagen, which results in the formation of coagulum and/or fibron that seals the hole or puncture. HIFU has been observed to play an effective role in sealing vessel punctures of varying sizes.
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The clinical challenge is to position the applicator 20 over the vessel puncture 14 and apply the HIFU energy at the correct focal depth to seal the puncture 14 without damaging the surrounding tissue 18. This is clinically challenging because the vessel puncture site 14 is distinct from the skin puncture site 15. Thus, the lateral and longitudinal alignment of the applicator 20 with the vessel puncture site 14 is not straightforward.
Theoretically, the image array 23 can be used to guide the device over the vessel puncture site 14. However, the interpretation of exactly where the vessel puncture site 14 is relative to the applicator 20 can become complicated. Therefore, use of a probe 34 that can be slid over a guidewire 19 has proven helpful. The probe 34, as shown in
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If an imaging array 23 and video display 32 is used, the video data should be transmitted at a different frequency than acoustic energy transmitted by the transducers 38 or 37 to prevent acoustic crosstalk or interference between the TOF and imaging measurements.
A preferred method of generating the three-dimensional position data involves the use of a MDS algorithm as explained below. The local coordinates of the distal end 36 of the probe 34 are calculated at 55, preferably using a PST algorithm. The local coordinates are used in conjunction with image array data to confirm the location of the probe tip 36 with respect to the vessel opening 14 (see 56 in
The term “control circuitry” is intended to cover the software, circuitry, programmable memory, processors, microprocessor chips, boards or other processing means indicated schematically at 30, 30a in the drawings that (1) convert the signals from the transducers into TOF calculations, that (2) convert the TOF calculations into three-dimensional position data and that (3) convert the three-dimensional position data into local coordinates. The location of the devices and software that perform these functions is unimportant. They may reside in the applicator 20 housing itself, in a separate controller box or panel 30 or a combination thereof.
More than one transducer 38 on the distal end 36 of the probe 34 can be utilized. The imaging array 23 could be eliminated or made redundant if the transducer 38 includes a pressure sensing capability or if a separate pressure sensing transducer was added to the probe end. A transducer 38 made from polyvinylidene difluoride (PVDF), polyvinylidene fluoride (PVF), PVDF piezo electric, PVF piezo electric or piezo electric copolymer materials can be utilized. PVD film, PVDF film, PVF piezo electric film, PVDF piezo electric film, copolymer film and piezo electric copolymer film transducers are known in the art. U.S. Pat. Nos. 6,835,178, 6,504,289, 6,485,432, 6,387,051, and 6,217,518 disclose such pressure sensing transducers. Instead of relying on the imaging array, the pressure transducer can be used to determine when the probe top 36 enters the opening 14 of the vessel.
In the example shown, four transducers 37a-37d are mounted directly on the applicator 20 as indicated in
Only three transducers 37 are required on the HIFU applicator 20. The use of four applicators 37 in this disclosure is an exemplary embodiment and allows for redundant calculations to increase the confidence of the calculated three-dimensional position of the distal end 36 of the probe 34 or the transducer 38 on the probe 34 and provide for the possibility of rejection of noisy measurements or in the event one or more of the transducers 37a-37d malfunctions.
The control circuitry 30, 30a utilizes a basic algorithm for determining if the three-dimensional position of the distal end 36 of the probe 34 with respect to the applicator 20. That basic algorithm may be a multi-dimensional scaling (MDS) algorithm. Given N reference transducers 37 mounted on the applicator 20 and one transducer 38 mounted on the probe tip 36, the input to the algorithm is a N+1×N+1 matrix of input distances as follows where Dij=the distance between the ith and jth transducer and Dij=0 because the distance of a transducer to itself is 0. It will be noted that only the last column and row of the matrix is actually calculated as the N×N sub matrix is determined by the mount location of the reference transducers 37.
The MDS algorithm provides an output matrix P of positions, i.e., DN+1×N+1→P3×N+1 wherein in each column of P is the x, y, z coordinates of a single transducer 37 position. In general, the output positions P have an arbitrary translation rotation and reflection. That is, there are an infinite number of output positions that match the input distances D. The positions P can be transformed to a local coordinate system of the applicator 20 using the procrustean similarity transform (PST) or other suitable algorithm. This algorithm matches the position of the two point sets from two different coordinate systems in a L2 norm sense. In this case, one would match the output positions of the N reference transducers 37 as provided by the MDS output coordinate system with the local coordinate system of the applicator 20. This would follow that registration of the applicator device 20 coordinates for both therapy and imaging with the three-dimensional position of the distal end 36 of the probe 34.
Thus, using three or more fixed transducers 37 mounted on the applicator 20 and at least one transducer 38 disposed at the distal end 36 of the probe 34, a more accurate distance calculation between the arrays 22 of the applicator 20 and the distal end of the probe 36 and therefore the puncture site 14 are provided. Therefore, a more accurate focal volume for the therapeutic arrays 22 can be calculated and the HIFU energy can be more accurately applied with minimal damage to surrounding tissue and organs.
Utilizing four or more reference transducers 37a-37d can provide a convenient redundancy. Specifically, because only three reference transducers are needed for an accurate calculation, the controller can perform the distance calculation multiple times and the results using a noisy or defective transducer can be ignored. Thus, the operator is assured that the calculation is accurate and not affected by transducer malfunction or noise.
While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure.
